A liquid crystal display (LCD) is a display apparatus without spontaneous light source. Thereby, a backlight source is needed for displaying function. The module consists of the whole set of backlight source is named a backlight module, which is comprised of a light source and an optical lens set. The optical lens set includes a light guide plate, a diffusion sheet, and prisms.
The main function of the diffusion sheet is to make the backlight source uniform. In conventional diffusion sheets, chemical particles are added to substrates of diffusion sheets as scattering particles. In current diffusion sheets, particles are distributed within resin substrates. When light passes through the diffusion sheets, it will continuously pass through media with two different refraction indexes. Thereby, light will encounter many refraction, reflection, and scattering. Consequently, optical scattering effect occurs.
In the following, a few recent inventions related to diffusers are taken as examples:
1. As described in the U.S. Pat. No. 6,888,663, clay is used as diffusion beads. After swelling and wetting treatments as well as interface quality improvement, thermal process is used to mix with polymer to produce the diffusion sheet. The advantage thereof is that only a small amount of clay (<3 wt %) is needed to produce decent effect (Haze˜80%, tranparency˜80%). In addition, inorganic materials have the advantages of ultraviolet, heat, and weather resistant. The drawback thereof is that clay will aggregate seriously, resulting in light scattering and reduction in transparency.2. As described in the U.S. Pat. No. 6,871,994, polymer beads are used as diffusion material. By adding adhesive, paint mixture is formed. Then it is coated on transparent polymer substrates to form diffusion sheets. The advantage of using polymer beads as diffusion material is that transparency is superior. However, the main disadvantage thereof is that polymer is not ultraviolet (UV) resistant. In addition, heat and weather resistibility and geometric stability is inferior to inorganic particles.3. As disclosed in Taiwan Patent Publication No. 200506035, a high light diffusivity, superior color tone light diffusing plate is shown. The advantage thereof is that heat and deformation resistibility of the light diffusing plate is maintained by adding organic UV absorber and stabilizer in process. The disadvantage thereof is that in the manufacturing process, in addition to adding diffusion material, other materials such as UV absorbers and stabilizers have to be added as well, which will complicate the system and hence will affect stability thereof. Besides, the overall material cost will increase accordingly. Another advantage of using organic absorbers is their deterioration after absorbing UV light.
According to the analysis described above, the present invention combines the advantages of the organic (polymer) and inorganic (clay) materials described above to design reflection, UV, heat, and weather resistant diffusion beads. Nanoclay can be applied to diffusion beads of diffusion sheets with the effects of reflection resistibility and UV light isolation. Reflection resistibility in diffusion sheets can enhance utility rate of light sources, and thereby increases luminance of the overall module. In addition, UV light isolation can lengthen lifetime of the diffusion sheets. Thereby, when applying nanoclay to diffusion sheets, reflection resistibility and UV light isolation, as well as light diffusion effect, can be attained.
The diffusion beads according to the present invention have a core-shell structure combined by organic and inorganic materials. They are heat and weather resistant. In addition, because of the multi-layer structure, they have the advantage of multiple light scattering. That is, in terms of the performance of the diffusion sheets, the usage of materials is less and the thickness of the diffusion sheets is thinner. Consequently, the diffusion beads according to the present invention conform to the market trend of lightness, thinness, and low cost. Furthermore, because the diffusion beads according to the present invention have formed a core-shell structure, the material of the outermost layer can be designed to be compatible with substrates with other materials. Thereby, the problems of dispersion and aggregation do not exist, which is another advantage of the present invention.